1. Field of the Invention
The invention relates to a natural fibre based, melt processable composite material comprising a polymer matrix of a biopolymer, and a reinforcing and filling agent.
2. Description of Related Art
Composite materials comprise an aggregate of a polymer and a fibrous reinforcing agent, in which the polymer acts as the binding element, or the matrix. The function of the reinforcing agents is to bear the mechanical loads to which the composite is subjected and to act as a stiffening and reinforcing component in the structure. In biodegradable composite materials, natural fibres are used as reinforcing and filling agents, including primarily, for example, wood fibres from various wood species, sawdust, flax, hemp, cotton, or sisal fibres. As the matrix, biodegradable polymers are used, such as polylactide as well as starch and cellulose based biopolymers.
For example the publication Mohanty, A. K., Misra, M. and Hinrichsen, G., “Biofibres, biodegradable polymers and biocomposites: An overview”, Macromol. Mater. Eng., Vol. 276/277 (2000), pp. 1-24, discloses biocomposite materials, in which a biodegradable polymer is used as the polymer matrix, and natural fibres, such as flax and hemp, are used as the reinforcing agent.
A problem with the above-mentioned natural fibre based composite materials is that the natural fibres used absorb water, resulting in the biological decomposition of the composite material. Consequently, the biological strength of biopolymer based composite materials is poor. Biological strength means that the product made of the composite material should be durable in its normal use environment, but the material is still degraded (decomposed) when subjected to suitable conditions, for example composting conditions.
Furthermore, the development of natural fibre composites involves the challenge of providing good adhesion between the two chemically different materials. As a result of poor binding of fibres to the polymer matrix, the mechanical strength of natural fibre based composite materials is poor. The adhesion can be enhanced by various coupling agents to improve the compatibility between plastic and fibre.
Another problem with the above-described natural fibre composites is the fact that the above-described natural fibres are not necessarily suitable as such for conventional plastics processing conditions.